1. Field of the Invention
The present invention relates to semiconductor integrated circuits, and especially concerns those semiconductor integrated circuits which include at least an integrated injection logic and a high frequency bipolar transistor.
2. Prior Art
Integrated circuits are recently made to contain the integrated injection circuits and bipolar transistors of pnp and npn types, and further, resistors, diodes, capacitors, isolated crossing connection regions, and so on.
In general, inactive circuit elements such as diodes, capacitors and isolated crossing connection regions are formed at the same time when making bipolar transistors. That is to say, these elements are made for example by the following steps:
forming a p.sup.+ -type diffused region of a medium impurity concentration in an n-island region, at the same time with forming of the base regions of npn bipolar transistors, the island regions being formed at the same time with forming of island regions serving as the collectors of the npn bipolar transistors, and then
forming an n.sup.+ -type diffused region of a high impurity concentration in the p.sup.+ -type diffused region, at the same time with forming of the emitter regions of the npn bipolar transistors.
In such conventional forming of the diodes, capacitors and isolated crossing connection regions, there have been liabilities of defects of undesirable leakages between the n.sup.+ -type diffused regions and the n-type island regions thereby lowering the production yield of the ICs (the leakages are hereinafter referred as CE leak since they are leakages between the n.sup.+ -type diffused regions formed at the same time with the emitter regions and the n-type island regions formed at the same time with the collector regions). Furthermore, the resistors, which are generally formed by the p.sup.+ -type layer, have been liable to defects of time-deteriorations of insulation and voltage dependency of their resistances.
The cause and circumstances of the above-mentioned defects of the conventional ICs are elucidated more in detail in the following with reference to FIG. 1(A), FIG. 1(B), FIG. 2, FIG. 3 and FIG. 4 showing various parts of such conventional integrated circuits.
FIG. 1(A) shows a part of a sectional elevation view of the conventional IC, comprising a high frequency bipolar transistor at the right half part and a diode at the left half part. In the IC, a p-type silicon substrate comprises epitaxially formed island regions 4a and 4b isolated each other by the isolation regions 6, 6 . . . of p.sup.+ -type, the region 4b serving as the collector region of the high frequency bipolar transistor. In the island regions 4a and 4b, p.sup.+ -type region 2a of the diode and the p.sup.+ -type base region 2b of the bipolar transistor are formed at the same time by a known diffusion process. Then n.sup.+ -type regions 3a, 1a, 1b and 3b are formed by a known diffusion process to have shallower depth than that of the p.sup.+ -type regions 2a and 2b. The n.sup.+ -type region 1b formed in the base region 2b serves as the emitter region, the n.sup.+ -type region 3b formed in the collector region 4b serves as a collector contact region, the n.sup.+ -type region 1a formed in the p.sup.+ -type region 2a forms n.sup.+ -region of the diode and the n.sup.+ -type region 3a formed in the n-type island region 4a serves as a contact region therefor. Buried regions of n.sup.+ -type 5, 5 are formed between the bottoms of the n-type island regions 4a and 4b and the p-type substrate region 7. Electrodes 1', 2' and 3' are the electrodes of the emitter, the base and the collector, respectively. Electrodes 8, 9 and 10 are the electrodes of the diode. The electrodes are formed through openings of an insulation film 12.
In the above-mentioned construction of the conventional IC, the n.sup.+ -type region 1a of the diode part is formed at the same time with the diffusion of the emitter region 1b, and the depth and impurity concentration of these two regions 1a and 1b are the same. Similarly, the depth and the concentration of the p.sup.+ -type regions 2a and 2b are the same. On the other hand, for attaining a good high-frequency characteristics, thickness of the active base region 2b' which is a difference of the depths of the p.sup.+ -type region 2b and the n.sup.+ -type region 1b is designed very thin, for example about 0.2 .mu.m. Therefore, as a result of the design to make the active base region 2b' thin, the thickness of the remaining part 2a' of the p.sup.+ -type region 2a under the n.sup.+ -type region 1a becomes also about 0.2 .mu.m. The problem of the such thin remaining part 2a' is that, when the diffusion front of the n.sup.+ -type part 1a undesirably makes a partially deep diffusion 1a' as shown in FIG. 1(B) to penetrate the thin remaining part 2a', the diode formed by the p-n junction between the n.sup.+ -type region 1a and the p.sup.+ -type region 2a makes the aformentioned CE leak, thus making shortcircuiting in logic circuit and resultant defects in the IC. Such CE leak is likely to be caused by crystal defect in the semiconductor layer, oxide-induced stacking fault (O.S.F) or precipitation of heavy metal. Since the IC generally has as similar large number as that of the transistors, such defects are fatal to the IC. Thus, the CE leak in the diode part has been a large problem in manufacturing yield of IC industry.
FIG. 2 shows another part of the conventional IC, where an isolated crossing connection region is formed and the undesirable CE leak is likely to occur causing defect of the IC. The isolated crossing connection region is formed mainly by an n.sup.+ -type region 1a' and auxiliarily by a p.sup.+ -type region 2a'+2a", and electrodes 13 and 14 are connected to both regions at the opposite ends thereof. Over the surface of the n.sup.+ -type region 1a', the insulation film 12, for example, SiO.sub.2 film, is formed, and over the insulation film 12a metal wiring 15 is formed, in a manner to be isolated from the connection regions 1a' and 2a' and crossing over them. In this construction, a p-n junction between the p.sup.+ -type region 2a'+2a" and the n.sup.+ -type region 4a is used negatively biased so as to isolate the connection region 2a'+2a" from the island region 4a'. Since the n.sup.+ -type region 1a' and the p.sup.+ -type region 2a'+2a" are formed simultaneously with the n.sup.+ -type emitter region 1b and the p.sup.+ -type base region 2b, respectively, of the high frequency npn bipolar transistor of FIG. 1(A), the bottom part of the p.sup.+ -type region 2a' is formed very thin, similarly as the active base region 2b of the bipolar transistor of FIG. 1(A). Accordingly, the thin part 2a' is likely to be penetrated by irregular deep part of diffusion front of the n.sup.+ -type region 1a', thereby resulting in undesirable CE leak of the isolated crossing connection region, and resultant defect of IC function.
FIG. 3 shows another part of the conventional IC, where a capacitor is formed and the undesirable CE leak is likely to occur causing defect of the IC. The capacitor is formed by a p-n junction between the n.sup.+ -type region 1a and the p.sup.+ -type region 2a, and electrodes 17 and 18 are connected thereto. Capacitances of the capacitors in the IC should be around 30 PF, and such capacitance requires a size of about 100 .mu.m.times.100 .mu.m or more. In the conventional construction, where the p.sup.+ -type region 2a and the n.sup.+ -type region 1a are formed simultaneously with forming of the p.sup.+ -type base region 2b and the n.sup.+ -type emitter region 1b, respectively, the remaining part 2a' of the p.sup.+ -type region under the bottom of the n.sup.+ -type 1a is very thin, and therefore the thin remaining part 2a' is likely to be penetrated by irregular deep part of diffusion front of the n.sup.+ -type region 1a'. Thereby undesirable CE leak in the capacitor is formed resulting in leakage current and poor insulation part in the capacitor. Such CE leak makes defect of IC function.
FIG. 4 shows another part of the conventional IC, where a resistor is formed and the undesirable CE leak is likely to occur. The resistor is formed by a p.sup.+ -type diffused region 23 which is formed, for example, simultaneously with the p.sup.+ -type base region 2b of the bipolar transistor of FIG. 1(A). Electrodes 25 and 25' are connected to both ends of the p.sup.+ -type region 23 through the insulation film of, for example, SiO.sub.2.
Firstly the resistor part of the IC has such a problem that the insulation of the resistor is determined by the insulation at the part of the peripheral bottom part 26, not by that at the flat bottom part 27 of the p.sup.+ -type region. This is because the intensity of electric field becomes highest at the peripheral bottom part, especially when the diffused region 23 is shallow. Therefore, it is necessary to eliminate such weak point. Secondly the resistor of the IC has a problem of stability of the resistance. The epitaxial region 22 and the p.sup.+ -type diffused region 23 form a p-n junction inbetween, and therefore, depletion layer grows both into the p.sup.+ -type region 23 and n-type region 22 from the p-n junction 27, and the growths of the depletion layers are dependent to the voltage applied to the p-n junction 27. When the applied voltage becomes higher, the depletion layer grows more, and resultantly, the effective depth of the p.sup.+ -type region 23 becomes shallower. Thus, the effective resistance of the resistor in the IC is dependent on the voltage applied across the electrodes 25 and 25', and this causes a grave problem.